Although the present inventor is unaware of any portable, floating lifting devices for LASH barges such as the one he has invented, there are three other sorts of devices in use that have sufficient similarities as to bear discussion. These are floating drydocks, marina boat lifts, and sunken hull salvaging devices.
Floating drydocks, in general, have a cradle-like hollow hull that has floodable compartments. When the compartments are flooded, the vessel to be worked on is sailed into the cradle. Then the flooded compartments are pumped out to raise the whole drydock/vessel combination sufficiently that the vessel is out of the water or is raised sufficiently to be worked on. Generally the distance between cradle sides is somewhat greater than the vessel. In the spaces between the cradle sides and the vessel hull sides the workers have access to the vessel hull sides. See FIG. 1. But that working quarters often is cramped, some ordinary tasks are made difficult and some jobs are hard to do well at all.
With these floating drydocks, usually a blanket of wood is necessary as an interface between the vessel hull bottom and the dock surface on which the vessel hull is supported. When the wood blanket is in the form of loose blocks or beams, it is difficult to get all of them in just the right positions when the dock flotation compartments are to be pumped out to raise the vessel. And, often, the wood blanket gets all roughed-up so it needs replacement when a next vessel is going to be worked on. Notice also from FIG. 1 how difficult it must be to work on the vessel hull bottom when it is so near the water and so obstructed.
The floodable compartments of conventional floating drydocks extend laterally so as to be under the vessel to provide sufficient hollow space to accomplish the rising and sinking. The difference in buoyancy between these compartments is difficult to control during rising and sinking, especially when the drydock hull being flooded, or pumped also is being subjected to river currents. As a consequence, usually drydocks are confined to use at a single protected site. The ships to be worked on must be brought to the drydock site. Thus while a conventional floating drydock floats, it usually is moored at a site and is not "portable" in the sense that it cannot "make house-calls" on vessels in need of repair.
The following prior U.S. patents show drydocks:
Janicki, No. 126,146, issued Apr. 30, 1872; Drake, No. 3,276,211, issued Oct. 4, 1966.
Boat lifts, e.g, for very light vessels such as small sail boats and pleasure craft are shown in the prior U.S. patent of Kramlich, No. 3,265,024, issued Aug. 9, 1977.
In lifting sunken hulls, conventionally, slings are passed under the sunken hull and secured on the opposite sides to pontoons. The vessel hull is and/or the pontoons are pumped out and the slings are raised to raise the hull. A prior art sunken hull salvage device is shown in the prior U.S. patent of Gowen, No. 110,564, issued Dec. 27, 1870.
Others previously have provided hull-supporting cradles with interfacing surfaces shaped to fit at least some part of the hull they are supporting. The prior U.S. patent of Beale, No. 3,777,691, issued Dec. 11, 1973 provides an example.
A mechanical lifting device, but one using screw shafts and worm screws, for lifting a vessel, is shown in the prior U.S. patent of Turner, No. 47,501, issued Apr. 25, 1865.